Tramadol, systematic name (±)-cis-2-[(dimethylamino)methyl]-1-(3-methoxyphenyl)cyclohexanol hydrochloride, is a widely prescribed centrally acting analgesic, administered as a racemic mixture, for the treatment of moderate to severe pain. Acting weakly at the μ-opioid receptor it has been shown to be addictive and provoke abusive behaviour. Following oral administration its major metabolites are (±)-cis-2-[(methylamino)methyl]-1-(3-methoxyphenyl)cyclohexanol trivial name: N-demethyltramadol/N-desmethyltramadol (NDT) and (±)-cis-2-[(dimethylamino)methyl]-1-(3 hydroxyphenyl)-cyclohexanol trivial name: O-desmethyltramadol/O-demethyl-tramadol (ODT). Urinary excretion of tramadol shows wide inter-individual variation; reported excretory amounts for tramadol and the two main metabolites over 24-72 hours of: tramadol 12-32%, N-desmethyltramadol 2-31% and O-desmethyltramadol 5-15% (Grond and Sablotzki 2004). O-desmethyl-tramadol is a considerably more potent μ-opioid agonist than the parent drug tramadol and it has recently been found in legal herbal products under names such as “Krypton”. Abuse and reports of fatalities connected to O-desmethyltramadol intake make its analytical detection for toxicological purposes desirable, especially using the practical and relatively inexpensive immunoassay technology. To date immunoassays have emphasised the detection of parent and metabolites (Table 1).
TABLE 1Cross-reactivity and sensitivity (IC50 in ng/ml) comparisons of Tramadolcommercial immunoassaysAnalyteRandoxBio-QuantImmunanalysisNeogenIDS% Cross-reactivityTramadol10013100100100NDT4<5 446 <2ODT57100 627 40Sensitivity0.275 200*5 200**cut-off value
EP1988398 describes a method for the detection of tramadol, N-desmethyltramadol and O-desmethyltramdol, the assay being specific to tramadol with cross-reactivity to N-desmethyltramadol and O-desmethyltramdol,